Collet



Nov. l2, 1929. B. F. sTowrsLl. y 1,735,804

COLLET Filed May 18, 1929 3 Sheets-Sheet l Nel a T D) INVENToR.

. ATTRNEYS.

Nov. 12, 1929. B, F, STQWELLv 1,735,804

COLLET Filed May 18, 1929 3 Sheets-Shea?, 2

, w Mu w. @f v 9. wma

f ATTORNEYS.

Nov. 12, 1929. B. F. sTowELL. 1,735,804

COLLET Filed May 18, 1929 s sheets-sheet 5 A TTORNEYS.

Patented Nov. 12, 1929 ria-5.a

BYRON? SIGZ'EIiIu,l 0F SPRINGFIELD5 MASSACHUSETTS, ASSIGNOR. TO VAN: NORMAN MACH-LNE TOOIjnGOM'PfANY, OF SP4RINGFIIELID, MASSACHUSETTS, A1 CORPORATION OF Application filed: May 18,

'l'hisinventionrelates to the improvement offcolletsotithe double end'type. Ithastor itsv principal object theproduction ot'a collet of this general' type having, a much` greater range ot-adjustmentthan hasbeenattainable informer collets. Aurther o bjecti's to, preserve substantially the same degreeot accun racy at all'y conditionsof adjustment of the Collet. The exact meaning of these objects, as Well asthe manner of theirl attainment, Will beclear from, the following description.

This. application. is a.. continuationl iny part of, my. priorV copending application Serial No.. 246,011, filed 'January 11,11928.A

Referring to the. drawings Fig. 1 ijs a. diagrammatic perspective vi'evv.. partly i'n section',v illustrating the. improved colletand its manner of use; i

Figs., 2. and 3 are respectively end and side .views showingl the ,blank from WhichY the im,-

proved collet ismade; v A

` Figs. ,4s to 7 are diagrammatic viewsillustrating successive, stages in tliemanufacture ot acollet according.;tomyi'nvention; y

Figisanvend vieW of, a chuck for holding tliefcollet during the grindingot its ends;

Fig. 9. is. a` diagrammatic side elevation showing the grinding operation.;A

10iis.an .enrl. elevation, onY an enlarged scale, showing the collet before`4 the initial grinding of its ends,l the collet being considered. in. this and .in subsequent similaiI views ashaving itsportionsadjacent one end only visible; i

Fig. 11 is a side elevation of one ofthe members or, brancheso, the rc ollet in` they condition. shown. inFig 10,;

Figs.. 12, and 1X3, are similar viewsshowing the initial grinding off one end ofthe collet;

Figrl isanlenlargedsection on line 14--14 ot" Fig., 12, showingthecollet as in contact Witliitsouter cone;

Eig. li's asimilar enlarged section: on line 15,-.-15l of Fig.. 12.3,

Fi'g 16 is a View similar to Fig. 121 but sb owing the collet expanded Figs. '1%7, and 1x8, areA views similar'to Figs L41, and' 1.5., but, are. taken respectively on. lines 1.7:-17, and, 18f1.8,0f`Fg161;.

FigT 19. isavi'ew corresponding toiaporton COLLET 1929iY serial` No. 364,128.

ot Fig. 1.2.,but, illustrating the etlectofv a, olisl tortion inf one of the colletbranclies; y

Fig. 20 is a section on line 20-20 of Figf. 17, showing the normaluexpansion ofv a; collet branch againstv the outer cone; FigQl isa similar view showing the eiect on the expanded collet of. grinding one ot the collet branches inthe distorted condition of Fig. 1-9;

Figs.` 22, and 23. areV views corresponding generally to Figs. l2aznd l'f-butillustrating the manner ot giving-aVVV preferred second grinding to theendofthe collet; and

Fig. 24isa section on.line.24'- 24 of'Fig.. 22 showing the preterredvaay of giving this second grind. Y l Y `While the details of the invention can be understood best `from the other `figures-,wits environment will be rst considered-With ret# erence to. Fig. 1r. VThe collet, SOisishovv'nfas c Vtraces 32 and 341 can be causedtoapproaclr or to recede trom4 each other, and therefore to exert a contracting forcev upon the ends of the colletv in4 a. Well known" manner. The

sleeve Simay be supported upon` a'headl'? t suitably provided with Work feedingandindexing devices by means ot- Which-the-Work, such as a valve, may be positioned in proper relation to atool suchv as a grinding Wheel 3S.

While they collet of inventionI is Vof utility in holding any type ot cylindrical Work-pieces, and in this use possesses a range. 1

of adjustment entirely beyond anything possible With double endcolletsof previous de'- signsait isotparticular utility indeailing-vvith a. type of' gasoline engine valvevvhich. has recently. comeinto use Thistype of, valve liasa hear iQ/a cylindricallshank 40, andan integral tappet block 41 formed atthe endof used. It is perhaps best illustrated in itsy entirety in Fig. Formed from a cylindrical blank 42 (Figs. 2 and 3), Vcuts 43, made alternatelyv from opposite ends of the blankand extending parallel to its axis nearly but not quite the full length of the cylinder, divide it into end 'segments 44 Yand intermediate bridge members or connecting bars 45. The segmentsare preferably three in number at each'end, and the segments lofthe two sets rare staggered with relation to each other. At

' this point, however, the resemblance between the improved collet and those of earlier design ceases.k The former designs `were not capable of anything like the range of adjustnient which is possible with my improved col- 'lotand the description willbe continued with especial reference Vto'*those features fwhich make possible both the range of adjustment and the preservation ofthe inherent accuracy of the collet throughout this range.

Thefirst feat-ure of construction to be considered under this headis the hardening and tempering of the collet. This can best be understoodb'y a reference toFigs. 4 to 7 inelusive, -where the various steps of 'forming and hardening vthe'collet are shown. Startin g with the'cylindrical blank 42 ofFigs. 2 and 3,

thel first operation is to cut the slots 43. This may' be done witha straight or beveledcutter, but is p'referablyi'done with a lrounded seY that it can be removed from'the arbor.

the arbor and the collars are suitably slotted cutter as shown so that abrupt changes in angles are avoided and a more even flexibility given to the bridge members 45 lwhere they join onto the end segments. During the operation of cutting the slots, the blank is held to an arbor 46 by opposed collars 47, each having an internally tapered surface '48 bearing against the end of the blank. One of the collars is held to the-arbor against a yshoulder thereof and is positioned by a key 49; the other is adjustably held by a lock nut 50 so Both to permit the passage of thecutting tool. It will be noted that the collars clamp the blank firmly against the arbor, preventing any vdistortion or Vshifting of the segments of the collet as they are being cut.

The slotted blank is .then placed upon a tube 51 (Fig. 5) to which it is clamped by collars 52 secured to the tube as by set screws F53 and having bearing surfacest54 for the ends of the blank, The tube with the blank clamped upon it is then placed in armufflev or is otherwise suitably heated to the proper but preferably they are left in placeinorderk to further guard againstl warping.

' It is now necessary to draw the temper of the connecting bars 45 so that they will be springy and'not brittle. This operation is also preferably utilized for thepurpose of giving a slight outward bow to the bridge members which has several desirable features. In the first place, the bowing serves to localize thepressu're of the finished ycollet on the work piecev within an area adj acent. the ends of the collet jaws, thus increasing the accuracy with which the work piece is held. In the second place, the bowing prevents any friction between the center section of the collet and the work piece which would introduce difliculties into the insertion or removal ofV work pieces ,fromV the collet. Again, as a corollary to the statements above, the bowing, by preventing vcontact of the center of the collet with the workpiece, eliminates the necessity of accomplishing these 'objects by machining the inner surface of the collet blank. Y '1 (y In tempering the collet blank, a tube 5,5, of a length less than thatvof the blank, is insertedin the center of thebo're; and arbors v5,6, ofV a diameter slightly less than'that of the tube 55, are inserted inthe ends. Chuck devices 57, having jaws 58, are secured to the arbors and clamp the end sectionsof the collet:

blank firmly against the arbors to hold them 1 Vagainst any r warping lor.` distortion. i Prefy erably the arbors are supported in guides 59 so that they may be rotated as a fiame is directed againstthe central part of the 'collet to supply the necessary tempering heat.

llxhenthe cor-rect heat has been reached,`in-

dicated by the color of the collet,the collet is `cooled to preserve the desired condition of continued until the inne-r surface of keach of' the end segments of the collet hasfbeen rsmoothed off substantially all the way across.

hen-thev collet is'in its normal expandedk position the geometrical axes of the" several Vfaces 66, which are each curved transverselyV of the member in the form of a fragment of,

a surface 'of revolution (in this case a cylinder), are all coincident with the axis of the collet as a whole, while'the individual geometrical axes 75 of the several outer faces 68 are spaced substantially symmetrically (Fig. 16) about this common axis. When thecollet is compressed, as in Fig. 12, the geometrical axes of the faces 68 merge with the axis of the contracted collet, which vis then coincident with the axis of the arbor or work piece upon which the collet is held, so Vthat the edges 7,1 of the faces 68 appear in this figure as concentric with each other; whereas the individual geometrical axes Geef the faces 66 become spaced substantially symmetrically with respect to this central axis.r The expanded and contracted positions of the Vcollet referred to are of course not denite limits of movement. these terms beingused to refer to the differing positions at which the inner and outer faces are ground. v

As long as there is no distortion of the collet in opening or closing, the structure shown is accurate throughout its entire range of adjustment'. If the precautions described above wit-h regard to the manner of holding -the'collet during the hardening and temper-` ingoperations are followed, the great majority ofcollets produced by this method will `require no further treatment. A certain'proportion, however, will acquire during hardening and tempering a strain which will cause a slight variation from the trueposition of the segments as they pass from one extreme of position to 4the other.` This variation will not begreat enough to be apparent to the eye, but it will be relatively large inlview of the necessity of preserving the accuracy of alignment of work held by the collet to the order of magnitude of a thousandth of an inch.

The reason for the variation in alignment will be Vconsidered with particular reference to Figs. 19,20 and 21, and themannerin which the effect is eliminated will Vthen be described. It must be stated first that the figures are suggestive only, as the magnitude of the inaccuracy is such that it could be positively shown in the drawings only by the use of a prohibitively large scale. collet segments are free'from disturbing strains, they will be symmetrical with respect to the work piece or arbor, both when contracted as in-Fig. V12 and when expanded as in Figs. 16 and 20. If, however, one of the segments is subjected to a strain causing it tofdeflect from its true position when contracted, a condition will result which is shown greatly exaggerated in Fig; 19. The inner If the surface 66 of the colletsegment was lapped true upon an arbor 'of the diameter vof the largest work piece for which the collet is designed, and'is, therefore, concentric with the arbor and with the other segments at this diameter. The distort-ion resulting from the deflection of the segment to the diameter of the small arbor 63 on which the collet y.is mounted .for grinding will cause the Ainner surface 66 to be asymmetrical with respect to the surface of the arbor 63, as is clearly shown in Fig. 19. The surface 66 and the surface of the arbor are necessarily eccentric owing to the difference in their radii, and the asymmetry referred to is evidenced by the center of the Vsurface 66 not contacting with the arbor, and by the centers 64 and Y75 of the segment and arbor respectively not being in line with the center of thesurface 66.

i The segment beingclamped in this asymmetrical position by the chuck 61, the grinding of the outer surface 68 will likewise be both eccentric and asymmetrical with `re spect to the inner surface 66. This is shown in Fig. 19 by the position of the line 71 representing the intersection of thev surface 68 vwith the yendof the collet segment. When the collet so ground is expanded, the inner surface will resume its symmetrical position with respectV to the large arbor or work piece 76, while the ground outersurface 68 is eccentric with respect both tothe arbor and to the enveloping conical surface 32.y This condition results in the outer surfaces 68 of the several sec-tions making contact with the enveloping cone'under non-uniform conditions. cone until the segments are all in contact As the collet is forced againstlthe both with the cone and with the work piece,

the work piece will be shifted sideways a .slight amount until this state of contact will result. This means that the work piece and the cone willk be eccentric with respect Ito each other, and as the cone is necessarily the definitelylocated part of thecollet assembly, thev work piece will be held or. rotated yin an eccentric manner. y. To remedy this defect in cases where it arises, I have devised the following corrective treatment, which is so simple that it is generally cheaper to treat all the collets under manufacture than vto test'them to see which ones are sufciently free from error-to' make treatment unnecessary.y The treatment consists in clamping theV collet, already ground upon the small arbor 63, to a large arbor 77, and in then giving to the outer surfaces 68 glio a slight second grinding in a manner similar to that in which the first grind was given.

Since the second grinding is upon alarger radius than that of the originally ground surface, it is apparent that only the center, or high area, of the surface 68 Will he affected. The surface ground on the second i operation is indicated in Figs. 22 and 23 at 79. l These figures show the area 7 9 as being in the center of the collet segment; but it Will be understood that' in the case ofy a `distorted segment such as that shownin Fig. 19, the regroundarea Will be tofone side or the other of the center. prepared in accordance With this disclosure, it is interesting to seethe varying -positions of the reground areas of the several segments, depending lupon the amount of distortion present in each segment.I The regrinding is preferably done on alarge arbor of substantially the same size astthe lapping arbor 60, but the exact size` is not of importance as long as it is near the diameterof the largest Work piece With which the collet is intended to deal. v

f Iny collvets so subjected to a double grinding, each yend segment Will have its outer socket-*engaging face built up of a median portion 79 and a marginal portion 68,. The median portion 79 is a fragment of a surface of revolution (preferably spheroidal), Whose geometrical yor generating axis is coincident when the collet is expanded with the axis of arbor 77 and, therefore, With the geometrical axes of the inner faces y66. The marginal'portion 68 is the residue Aofthe surface resulting from the grinding operation shovvn in Fig. 8,fand When-the colletis contracted hasits geometrical axis coincident with that of the small arbor 63. When'the collet is expanded, the individual geometrical axes of the marginal portions of `the several segments fare spaced about'the axis lof the collet as shown at in Fig, '22. In the lcase of distorted segments'the so-call'ed median Vportion will not beexactly in the center of the socket-engaging face, but it Will have ythe geometrical or generating axisof the surface of revolution of which it is a fragmentdisposed as stated. At small diameters, the surface 68 provides the contact with the eneveloping cone 32, but it is replaced in this regard by the surface 79 at large diameters. The'work piece held by the collet Will thus be concentric in both' extreme conditions.:v Ordinarily this Will be suiiicient to keep the errors belovv thevalue at which they become of import 5d ance; but ifa still further refinement is de sired, onev or more additional 4regrindings may be given-at intermediate diameters. rlhe lresult of this Will ofcourse be to cover the tapered end surfaces of the collet'l segments with a plurality of ground surfaces, each of which is'strictly accurate at but one diameter, but the maximum error of which can be kept yWithin any assigned limits.

Preferably the grinding Wheel which -is used to give the regrinding described has a A radius of curvature of its shaped grinding face slightly greater than that by Whichtlie rst ground surface Was generated. The ground surface 80 will be slightly flatter than ithe surface 69, as shown in Fig. 24. This In actual inspection of colletsv is not essential, but gives adesi'rabl'el condi.- tion as it Will be apparentfrom Fig; 17 that `the point of'contact. between the collet. and

the cone when the collet is expanded is rather close to the outer edge of ythe ground sur face. rlhis change Ain the radius of the generated surface thus increases the size of the reground area in the direction where :it gis most needed..` '1 w n Claims':.A l, f

l; A chucking device of the ytype adapted for use ,with opposedy relatively movable Y sockets of generally .conical internal form and comprising a tubular member khaving slots extending alternately from opposite ends of the member nearly the entire length thereof to provide .end'segments joined by flexible connecting bars, in which the end segments are hardened to give vpermanence to` their surface formation andthe connecting bars are tempered tofpermit a controlled expanding andcon-.tracting `movement of the vso end segments of a 'considerable amplitude,

beras av Whole, While Vthe :socket-engaging faces have their individual geometrical Aaxes spaced about said commonfaxis, and when the member is contracted the socketengagmg faces have :their geometrical axes all coinci-` dentvvith the axis of the member as ya vvhole, While the Work-gripping faces have their individual geometrical axes k'spaced about saidcommon axis., j ,v l ,A i

2. A chucking deviceof the type adapted for use' with opposed relatively movable sockets of generally conical internal form and comprising a tubul-ar member having slots extending alternately from 'opposite ends of the member nearlythe entirelength thereof to provide `end segments joinedby flexible connecting bars, in which the end segments are hardened :to give `permanence to their surface formation andthe connecting bars are temperedto permit a controlled ex:-

panding andcont-rfacting ymovement ,of the;

end segments ,of a considerable amplitude,

and in which the end `segments each have y inner work-gripping Afaces curved transverse lyv of the kmember inthe form of surfaces of revolution, and .outer socket-engaging faces...y

curved both transversely and longitudinally ofthe member in the form of vgenerally `,sp-hee' roidal surfaces of revolution tapering off in size towards .the ends `of ,the member, said;

Work-gripping :and socket-engaging 'faCSS b6- in'g so formed that when the member-is inexpanded condition the Work-'gripping faces have their geometrical axes all coincident with the axis of the member as a'vvhole, vvhile the. socket-engaging faces have their inindivi'dual geometrical axes spaced about said common axis, and When the` member is contractedA the socket-engaging faces have their geometrical axes all coincident With the axis of the member as a Whole, While the Workgripping faces have their individual geometrical axes spaced about said common axis. 3. A chucking device 0f the type adapted for vuse with opposed relatively movable 'sockets ofgenerally conical internalfform V metrical axes spaced about said common axis,

and `when the member is contracted the marginal portions of said faces have their geometrical axes coincident With the axis of the member as aV Whole While the medianv portions have their individual geometricalV axes spaced about said common axis.

14. A chucking device of the type adapted l for use With opposed relatively movable sockets of generally conical internal form and comprising a tubular member having slotsextending alternately from opposite ends of the member nearly the ent-ire length thereof to lprovide end segments joined by flexible connecting bars, the inner Work-engaging face of eachV of said segments being curved transversely of the Amember in the form of a surfacey of revolution and the outer socket# engaging face of each ofY said end segments being tapered off toward the adjacent end of the member and having median and marginal portions shaped as surfaces of revolution of different curvature characteristics, the several faces being so formed that-When the member is inexpanded condition the Work-engaging faces and the median portions of the socket# engaging faces have theirv geometrical axes substantially coincident with the axis of the member as a Whole, While the marginal portions of the socket-engaging faces have their individual geometrical axes spaced about said common axis, and when the member is contracted the marginal lportions of said faces have their geometrical axes coincident with'A the axisl of the member as a Whole While the Work-engaging faces and the median portions ofthe socket engaging faces have their indi vidual geometrical axes spaced about said common axis.

5. kA chucking device of the type adapted for use with opposed relatively movable sockets of generally conical internal form and comprising a tubular memberhaving slots extending alternately from opposite ends of thev member nearly the entire length thereof to provide end segmentszjoined by flexible con# nectingbars, in which the end segments are hardenedto give permanence to their surface formation and the connecting bars, are tempered to permit a controlled expanding and contracting movement of the end segments'of a considerable amplitude, the inner Work-en-V gaging face of each of saidl segmentsbeing curved transversely of the member inthe form of a-surface of revolution, and the outer socket-engaging faces being `curved' both transversely and longitudinally of the member with a tapering 01Ty in size towardsrthe ends of the member and lhaving median and marginal portions shaped as generally spheroidalsurfaces of revolution of different curvature characteristics, the several faces being so formed that When the member lis in expanded condition'the Work-engaging faces and the median portions of thesocket-engaging faces have their geometrical axes substantially coincident with the axisof the member as a Whole While the marginal' portions of the socket-engaging faces have their individual geometrical axes spacedk about said common axis, and When the member is contractedV the marginal portions of said faces have their geometricaly axes coincident With the axis of the member as a Whole Whilevthe Work-engag ingv faces and the median portions ofv the socket engaging faces have their individual' geometrical axes spaced about said common axis. l i

` 6. A'chucking-device ofthe type adapted for use With opposed relatively movable sockets of generally conical internal form and comprising a tubular member havingslots` extending alternately fromv opposite ends of the member nearlythe entire length thereof to provide end segments joined by connecting bars, the outer socket-engaging face of-each Y of said end segments being formedWith a pluralityl of surface portionsfof kdifferent curvature characteristics, one of such portions contactingvvith the socket When the member is expanded and another contacting with the socket lWhen the member is conf,

tracted.

In testimony whereof I have affixed my sig` 4 BYRON F. sTovvnLL.V ,i

nature. Y

izo 

